1. Field of the Invention
The present invention relates to a method for code protection using an electronic key system for a motor vehicle having a built-in central electronic lock, the electronic key comprising a transmitter which generates a coded infrared signal that is picked-up by an electronic lock receiver tuned to the coded infrared signal. Identical sequences of codes or code words are stored or generated in both the transmitter and receiver. The transmitter and receiver are automatically set to a new coinciding code or code word after each transmitting or receiving event, respectively.
2. Description of the Prior Art
With electronic keys that employ a transmitter that beams out a coded infrared signal which is subsequently decoded by a receiver of an electronic lock, there is a danger that the coded infrared signal can be intercepted or otherwise picked-up by a random receiver. The intercepted signal can be stored and then later reproduced so that unauthorized persons are also able to activate the electronic lock and thus open, for example, the lock of a motor vehicle.
The coded infrared signal can be intercepted by having the intercepting receiver located within the emission range of the infrared transmitter, or by receiving the coded infrared signal after it has been reflected from a surface such as glass.
The possibility of interception of the coded infrared signal can be minimized by bringing the transmitter and receiver into close proximity with each other so that a second intercepting receiver does not lie within the emission range region of the transmitter. However, with motor vehicles, since the electronic lock receivers are located within the interiors of the vehicles, there is always the danger that the infrared signal will be reflected off of the windows of the vehicles, and thus, the interception of reflected signals cannot practically be avoided. Additionally, requiring placement of the transmitter in close proximity with the receiver runs contrary to the easy manipulation and use of such electronic keys and locks, as one can no longer activate the electronic lock at a distance.
An electronic key system in which it is possible to adjust the authorized code at both the transmitter and receiver by way of switches is known from British Letters Patent GB No. 2,051,211A. Because the code can be changed often by means of changing the switch settings, unauthorized activation of the electronic lock associated with the key can be made more difficult. A danger exists, however, that the transmitter and receiver can be set to different codes so that activation of the electronic lock is no longer possible. Experience has also shown that a user is not likely to set a new code at the transmitter and at the receiver after each unlocking event, so that unauthorized activation of the electronic lock, for example of a motor vehicle, by means of reproduction of an intercepted signal, is not impossible.